A typical vehicle occupant restraint system comprises a container, an inflatable air bag disposed in the container, and an inflator in proximity to the inflatable air bag. The inflatable air bag is commonly formed of flexible fabric material such as nylon, and is generally stored in the container in a collapsed, folded condition. The air bag has a fluid inlet opening through which fluid (e.g., gas) under pressure can be directed into the air bag. The perimeter of the fluid inlet opening (often referred to as the "mouth" of the air bag) is attached to the container and/or the inflator.
At the onset of a collision, the inflator is actuated and rapidly directs an inert, non-toxic gas (e.g., nitrogen) into the fluid inlet opening in the air bag. The gas forces the air bag out of the container and rapidly inflates the air bag to a predetermined configuration. When inflated to its predetermined configuration, the air bag cushions a vehicle occupant against impact with a structural part of the vehicle
In the construction of an air bag, one of the fundamental considerations is the design of the mouth of the air bag. The mouth of the air bag must provide a fluid inlet opening and a means whereby the air bag can be attached to the container and/or inflator.
One known type of design for the mouth of an air bag is disclosed in Goetz U.S. Pat. No. 4,817,828. The air bag fabric is formed into tubes at the perimeter of the fluid inlet opening A series of rigid retaining bars are disposed in the fabric tubes to complete the mouth of the air bag. The air bag is attached by fasteners to a reaction can that is part of a container for the air bag. The fasteners secure the retaining bars to the reaction can with part of each fabric tube captured between the reaction can and a retaining bar. The retaining bars distribute forces on the air bag material and thereby help it resist being torn away from the reaction can during deployment of the air bag.
Another known type of design for the mouth of an air bag is disclosed in U.S. Pat. No. 4,183,550. The fluid inlet opening is a generally circular opening in the air bag fabric. The opening has a diameter smaller than the outside diameter of an inflator designed to be inserted into the air bag. An inner portion of the bag material about the opening has radial slits and extends inwardly of a retainer which is used to mount the air bag in an occupant restraint system. The structure allegedly (i) enables the inflator to be inserted into the opening in the bag material, and (ii) increases the shear resistance of the air bag material in the area of the air bag surrounding the inflator.
Both of the foregoing patents disclose mounting structure for the mouth of an air bag designed to resist tearing of the air bag away from the remainder of an occupant restraint system during deployment of the air bag. Typically, in vehicle occupant restraint systems incorporating a pyrotechnic inflator, such as in the preferred embodiments of the Goetz '828 patent, the mouth of the air bag is spaced outward from the inflator. That spacing provides some protection against the heat of the inflator (or of the gases generated by the inflator during its operation). Additionally, it is known to coat the fabric of an air bag material with a heat resistant material, to provide further heat protection to the air bag fabric.
In the air bag system shown in the '550 patent, which also incorporates a pyrotechnic inflator, the inner ends of the air bag lie directly against the inflator. Moreover, the gas outlet holes in the inflator are uncovered and are located so that gas directed from the holes can impinge directly on the mouth of the air bag. Thus, there is a risk that the heat of the inflator or the gas directed from the inflator may burn or melt the mouth of the air bag. When weakened by burning or melting, the mouth of the bag may tear away from its fasteners under the pressure of deployment of the air bag.
As vehicle restraint systems become more compact, the air bag is necessarily located nearer the inflator. Thus, the need to provide air bag designs which resist both the heat and pressure of deployment becomes particularly important. Moreover, since inflatable air bags are being installed in more vehicles, the need to efficiently produce such air bags and to incorporate them efficiently into occupant restraint systems is becoming increasingly important.